1. Field of the Invention
The present invention relates to a production order determining method for determining a production order of a plurality of production types of products in a production line where a production information is given in the form of specified periods of time of production with respect to production types of products.
2. Description of the Prior Art
Japanese Patent Publication SHO 63-265791 discloses a method for determining a production order of different models or production types of engines, in an engine assembly line, which are to be supplied to different car assembly lines. In the prior art method, the production order of the different production types of engines at the engine assembly line is determined based on input requirements from the respective car assembly lines, which are given in the form of numbers of each production type of engine to be supplied per successive fixed production periods (e.g., per shift or per day) to each of the car assembly lines. More particularly, a production period portion P.sub.i for an engine of each production type i is calculated from the input requirements. After a fixed value of P.sub.i has been calculated for an engine of each production type i, a production expectation value X.sub.ij for each production order j of each engine type i is calculated by the following equations: EQU X.sub.i1 =P.sub.i (1) EQU X.sub.ij =X.sub.ij-1 +P.sub.i -D.sub.ij-1 (2)
where, D.sub.ij is a variable having the value 1 in a case where an engine of production type i is produced at production order j and taking the value 0 in other cases. In the prior art, a production order j is determined so as to produce an engine of the production type i having the highest value of X.sub.ij.
For example, in an engine assembly line which receives requests from an A car assembly line to supply two a-type engines a day, from a B car assembly factory to supply one b-type engine a day, and a C car assembly factory to supply one c-type engine, a production order of the a-, b-, and c-type engines is determined in the following way. At first, a production period portion P.sub.A for the a-type engine is calculated by dividing the required number of a-type engines per production period (2 per day) by the sum of all a-, b-, and c-type engines required per production period:2/(2+1+1). The resulting value of P.sub.A is 0.5. Similarly, a production rate P.sub.B of the b-type engine is 0.25, and a production rate P.sub.C of the c-type engine is 0.25. Therefore, from equation (1), X.sub.a1 is 0.5, X.sub.b1 is 0.25, and X.sub.c1 is 0.25. Because the highest of these values is X.sub.a1, it is determined that the first type of engine to be produced each day is the a-type engine.
Then, X.sub.a2, X.sub.b2, and X.sub.c2 are calculated in the following manner: EQU X.sub.a2 =X.sub.a1 +0.5-1=0 EQU X.sub.b2 =X.sub.b1 +0.25-0=0.5 EQU X.sub.c2 =X.sub.c1 +0.25-0=0.5
Because the highest of these values is X.sub.b2 or X.sub.c2, either X.sub.b2 or X.sub.c2, for example, X.sub.b2, is chosen and the second engine to be produced each day is the b-type engine.
Similarly, EQU X.sub.a3 =X.sub.a2 +0.5-0=0.5 EQU X.sub.b3 =X.sub.b2 +0.25-1=-0.25 EQU X.sub.c3 =X.sub.c2 +0.25-0=0.75
Because the highest of these values is X.sub.c3, the third engine to be produced each day is the c-type engine.
Similarly, EQU X.sub.a4 =X.sub.a3 +0.5-0=1 EQU X.sub.b4 =X.sub.b3 +0.25-0=0 EQU X.sub.c4 =X.sub.c3 +0.25-1=0
Because the highest of these values is X.sub.a4, the fourth engine to be produced each day is another a-type engine. Therefore, the engine production order for producing four engines a day is determined to be an order of a, b, c, and a.
With respect to the second day, EQU X.sub.a5 =X.sub.a4 +0.5-1=0.5 EQU X.sub.b5 =X.sub.b4 +0.25-0=0.25 EQU X.sub.c5 =X.sub.c4 +0.25-0=0.25
Because these values are equal to the values of X.sub.a1, X.sub.b1, and X.sub.c1, respectively, the same order of engine production as that of the first day should be executed in the second day.
The reason why the above-described determination of a production order is possible is that P.sub.i can be calculated for the first day, and the same P.sub.i can be used for the second day, the third day, . . ., and the n-th day without varying the P.sub.i value. More particularly, the above described determination of a production order is possible or effective only for a production line where input information is provided in the form of a number of products to be produced per fixed production period (e.g., each day) with respect to each production type, because the production period portion P.sub.i used in equations (1) and (2) is fixed.
However, in a production line, such as a complete knock down line (a packing line where parts are packed in a domestic country and are shipped to foreign countries), where input information for a production order schedule is given in the form of usually different specified periods of time of production (in the case of a packing line, specified periods of time of packing, that is, information about how many of what type of boxes should be packed within what periods of time), the prior art production order determining method cannot be used, because fixed values of P.sub.i cannot be used in the above equations (1) and (2).